1. Field of the Invention
This invention relates to a motion detection circuit for detecting motion in a video signal and a noise suppression circuit including the motion detection circuit.
2. Description of the Prior Art
A motion detection circuit for detecting motion in a video signal from a difference signal between the video signal and the one-frame delayed video signal is known and a noise suppression circuit is also known. The noise suppression circuit includes the motion detection circuit, a circulation signal generation circuit for generating a circulation signal in accordance with the difference signal and the motion detection signal, and a subtractor for subtracting the circulation signal from the video signal to output a noise suppressed video signal. Such a prior art motion detection circuit and a prior art noise suppression circuit are disclosed in Japanese patent application provisional publication No. 9-81754.
FIG. 8 is a block diagram of such a prior art noise suppression circuit including a prior art motion detection circuit.
The prior art motion detection circuit includes a frame memory 610 for generating a delayed video signal from the noise suppressed video signal, a subtractor 602 for generating a difference signal (interframe difference signal) between the video signal Vi and the delayed video signal, a motion detection circuit 603 for detecting a motion from the video signal Vi and the delayed video signal to output a motion detection signal.
The noise suppression circuit further includes a subtractor 607 for generating the difference signal between the video signal Vi and the delayed video signal, a circulation amount determining circuit 608 for generating a circulation signal from the difference signal in accordance with the motion detection signal, and a subtractor 609 for obtaining the difference between the video signal Vi and the circulation signal to output the noise suppressed video signal.
The aim of the present invention is to provide a superior motion detection circuit and a superior noise suppression circuit.
According to the present invention, there is provided a first motion detection circuit including: a delay for generating a delayed video signal from a video signal, the delayed video signal being delayed by one frame from the video signal; an interframe difference signal generation circuit for generating an interframe difference signal between the video signal and the delayed video signal; an edge detection signal generation circuit for detecting an edge from the video signal and the delayed video signal and generating an edge detection signal; and a motion judging circuit for judging a motion in the video signal at a target pixel from the interframe difference signal in accordance with the edge detection signal to output a motion detection signal, wherein the motion judging circuit includes: a peripheral pixel comparing circuit for detecting polarities of the interframe difference signal at each pixel at a predetermined area around the target pixel, detecting a difference in the number between the positive and negative polarities of the interframe difference signal at each pixel at the predetermined area and an absolute value of the difference, obtaining a J-valued first result from the absolute value; and a majority detection circuit including a memory for detecting a majority of Q of the first results of the peripheral pixel comparing circuit at Q pixels around the target pixels and judging the motion in the interframe difference signal at the target pixel in accordance with the detected majority with deviation to a side of stopping to output a second result as the motion detection signal, J being a natural number more than one, Q being a natural number more than one.
The first motion detection circuit may further include a low-pass filter for low-pass-filtering the interframe difference signal; and a selector for supplying either of an output of the low-pass filter or the interframe difference signal to the motion judging circuit as the interframe difference signal in accordance with a selection signal.
In a second motion detection circuit, the motion judging circuit mentioned in the first motion detection circuit may further include a polarity deviation detecting circuit for detecting polarities of the interframe difference signal at each pixel of the video signal, detecting agreement of the polarities of all pixels at any of an upper left area of the target pixel, an upper right area of the target pixel, a lower left area of the target pixel, and a lower right area of the target pixel, and judging motion in the interframe difference signal at the target pixel to be moving in the presence of the agreement, each of the upper left area, the upper right area, the lower left area, and the lower right area including Mxc3x97N pixels of the video signal, M and N being natural numbers, wherein the polarity deviation detection circuit changes the second result from the intermediate movement to the stopping in accordance with the agreement to output the motion detection signal when the second result is indicative of the intermediate motion and outputs the motion detection signal with the second result unchanged when the second result is indicative of the moving and stopping.
In the second motion detection circuit, the upper left area, the upper right area, the lower left area, and the lower right area include the target pixel or are outside and adjacent to the target pixel.
In a third motion detection circuit, the edge detection signal generation circuit mentioned in the first motion detection circuit may include a first edge detection circuit for detecting an edge from the video signal, a second edge detection circuit for detecting an edge from the delayed video signal, a third edge detection circuit for detecting an edge from the video signal and the delayed video signal, and a switch responsive to a selection signal for outputting either of an output of the first, second, or third edge detection circuit as the edge detection signal.
In the third motion detection circuit, the edge detection signal generation circuit may be further responsive to a width control signal indicative of values of m and n and the edge detection signal generation circuit may detect the edge detection signal with a horizontal width of (2m+1) pixels and with a vertical width of (2n+1) pixels, the n and m are positive integers.
In the second motion detection circuit, values of the M and N may be controlled in accordance with the edge detection signal.
According to the present invention there is also provided a noise suppression apparatus including: a motion detection circuit including: a delay for generating a delayed video signal from a video signal, the delayed video signal being delayed by one frame from the video signal; an interframe difference signal generation circuit for generating an interframe difference signal between the video signal and the delayed video signal; a low-pass filter for low-pass-filtering the interframe difference signal; a switch for outputting either of an output of the low-pass filter or the interframe difference signal in accordance with a selection signal; an edge detection signal generation circuit for detecting an edge from the video signal and the delayed video signal and generating an edge detection signal; and a motion judging circuit for judging motion in a target pixel of the video signal from an output of the switch in accordance with the edge detection signal; a circulation signal generation circuit for generating a circulation signal in accordance with the interframe difference signal and the judged motion; and a difference signal generation circuit for generating a difference signal between the circulation signal and the video signal to output a noise suppressed video signal, wherein the motion judging circuit includes: a peripheral pixel comparing circuit for detecting polarities of the interframe difference signal at each pixel at a predetermined area around the target pixel, detecting a difference in the number between the positive and negative polarities of the interframe difference signal at each pixel at the predetermined area and an absolute value of the difference, obtaining a J-valued first result the absolute value, the polarity deviation detection circuit changing the first result to stopping in accordance with the agreement when the difference is judged to be an intermediate value among J values to output a second result; and a majority detection circuit including a memory for detecting a majority of Q the second results of the polarity deviation detection circuit at Q pixels around the target pixels and judging the motion in the interframe difference signal at the target pixel in accordance with the detected majority with deviation to a side of stopping to output the motion detection signal, J being a natural number more than one, Q being a natural number more than one.
In the noise suppression circuit, the circulation signal generation circuit may include: a coefficient generation circuit for generating a coefficient k, kxe2x89xa60 less than 1 in accordance with a judging result of the motion judging circuit; and a multiplier for multiplying the video signal by the coefficient k to output a circulation signal
In the noise suppression apparatus, the coefficient k when the motion judging circuit judges the motion to be stopping is greater than the coefficient k when the motion judging circuit judges the motion to be moving.
The motion detection circuit in the noise suppression apparatus may be replaced with each of the motion detection circuit mentioned above.